Temporary tattoos may one day power your wearable medical devices

If you’ve ever plugged into a wearable device in a doctor’s office, you’re familiar with electrodes attached to your body to monitor its electrical signals. The problem with these off-the-shelf electrodes made of metal or hydrogel is that they do not always stay in place during movement, for long periods or on sweaty or hairy skin.

Penn State engineers aim to change that by tattooing using conductive ink to power sensors for wearable devices such as electroencephalograms (EEG), electrocardiograms (ECGs), and electromyograms (EMGs) that track brain, heart, and muscle activity, respectively.

As stated in A paper Published Monday in the Proceedings of the National Academy of Sciences, the engineering team has filed a provisional patent for this ink, an aqueous solution mixed with polymers and acidic additives that starts out transparent with a glue-like consistency. It can be dyed with food dye to create different colors of a cute fox or shark that opens its mouth when you open your hand, and dries on the skin in less than 10 minutes. It can be reapplied or washed off later.

Thanks to their fun and customizable nature, these paintable electrodes could be especially useful for children who may be more likely to wear a medical device if supported by a temporary tattoo of their favorite character or animal.

How ink powers wearable devices

To connect the ink to the sensors, there is a porous silver fabric with electrodes attached. Before the applied tattoo dries, the fabric is placed over the design so that it adheres to the skin. Next, the fabric is connected to a port on a wearable monitoring device. The latter is glued to the skin under clothing.

Electrical signals collected by the ink are sent through the fabric to a monitoring device, which then transmits the data to a computer via Bluetooth.

“The big idea behind this is that in the future, you could potentially have a more expensive sensor module that remains separate from the system, but the electrodes themselves can be disposed of. One bottle of ink can provide enough material to coat multiple electrodes over the course of several days or a week.” Larry Chengcorresponding author of the paper and the James L. Henderson Jr. Memorial Professor of Engineering and Mechanical Sciences at Penn State, in A press release.

The hope is that these temporary electrical tattoos could help detect heart attacks early, read brain waves, or power robotic prosthetics.

Additionally, because it is drawn directly onto the skin, the ink is more durable and accurate than skin-mounted sensors, where there may be an air gap between them and the skin. As for silver fabric, because it is porous, its connective electrodes can expand to more than 150% of their original volume. This means that sweat can pass through the fabric without negatively affecting adhesion, accuracy or comfort.

What the team found during testing

Experimenting with the ink, the Penn State team found that the coated electrodes could monitor ECG signals for up to 12 hours. They also stayed during rehearsal. When applied to a team member’s forearm, the electrodes successfully tracked muscle signals using an EMG device, enabling remote control of the robotic hand.

Since the electrodes can be washed and reapplied, 12 hours is not the limit for their use.

Eventually, the coated electrodes could power sensors that track cortisol or glucose. The team is also looking at commercial use for clinicians, such as pediatricians. Or create “smart plants” that provide information on exposure to chemicals in their environment and their impact on plant health.

Just as it has become normal to see people wearing health trackers Smart watches and Smart ringsMaybe one day no one will bat an eye when they see someone leaving the doctor’s office with a temporary tattoo.